stacking t-3 and t-2?

any reason not to? t-2 is a metabolite of t-3 but hasn't lived up to expectations (while some what effective nothing mind blowing talking about san's 3,5 thyro-cuts 2). i hypothesis that having an increase in t-3 hence an increase in both t-2 metabolites taking additional 3,5 would have a synergistic effect? am i off? would taking t-2 have a negative feed back?